Luminescence and Structural Characterization of Gd2O2S Scintillators Doped with Tb3+, Ce3+, Pr3+ and F for Imaging Applications

none14siRadiodiagnostic technologies are powerful tools for preventing diseases and monitoring the condition of patients. Medicine and sectors such as industry and research all use this inspection methodology. This field demands innovative and more sophisticated systems and materials for improving resolution and sensitivity, leading to a faster, reliable, and safe diagnosis. In this study, a large characterization of gadolinium oxysulfide (Gd2O2S) scintillator screens for imaging applications has been carried out. Seven scintillator samples were doped with praseodymium (Pr3+), terbium (Tb3+) activators and co-doped with praseodymium, cerium, and fluorine (Gd2O2S:Pr,Ce,F). The sample screens were prepared in the laboratory in the form of high packing density screens, following the methodology used in screen sample preparation in infrared spectroscopy and luminescence. Parameters such as quantum detection efficiency (QDE), energy absorption efficiency (EAE), and absolute luminescence efficiency (ALE) were evaluated. In parallel, a structural characterization was performed, via XRD and SEM analysis, for quality control purposes as well as for correlation with optical properties. Spatial resolution properties were experimentally evaluated via the Modulation Transfer Function. Results were compared with published data about Gd2O2S:Pr,Ce,F screens produced with a standard method of a sedimentation technique. In particular, the ALE rose with the X-ray tube voltage up to 100 kVp, while among the different dopants, Gd2O2S:Pr exhibited the highest ALE value. When comparing screens with different thicknesses, a linear trend for the ALE value was not observed; the highest ALE value was measured for the 0.57 mm thick Gd2O2S:Pr,Ce,F sample, while the best MTF values were found in the thinner Gd2O2S:Pr,Ce,F screen with 0.38 mm thickness.De Martinis, Alessia; Montalto, Luigi; Scalise, Lorenzo; Rinaldi, Daniele; Mengucci, Paolo; Michail, Christos; Fountos, George; Martini, Nicki; Koukou, Vaia; Valais, Ioannis; Bakas, Athanasios; Fountzoula, Christine; Kandarakis, Ioannis; David, StratosDe Martinis, Alessia; Montalto, Luigi; Scalise, Lorenzo; Rinaldi, Daniele; Mengucci, Paolo; Michail, Christos; Fountos, George; Martini, Nicki; Koukou, Vaia; Valais, Ioannis; Bakas, Athanasios; Fountzoula, Christine; Kandarakis, Ioannis; David, Strato

Imaging performance of a CaWO4/CMOS sensor

The aim of this study was to investigate the modulation transfer function (MTF) and the effective gain transfer function (eGTF) of a non-destruc­­tive testing (NDT)/industrial inspection complementary metal oxide semi­conductor (CMOS) sensor in conjunction with a thin calcium tungstate (CaWO4) screen. Thin screen samples, with dimensions of 2.7x3.6 cm2 and thick­ness of 118.9 μm, estimated from scanning electron microscopy-SEM im­ages, were extracted from an Agfa Curix universal screen and coupled to the active area of an active pixel (APS) CMOS sensor. MTF was assessed using the slanted-edge method, following the IEC 62220-1-1:2015 method. MTF values were found high across the examined spatial frequency range. eGTF was found maximum when CaWO4 was combined with charge-coupled devices (CCD) of broadband anti-reflection (AR) coating (17.52 at 0 cycles/mm). The com­bi­nation of the thin CaWO4 screen with the CMOS sensor provided very pro­mis­ing image resolution and adequate efficiency properties, thus could be also con­sidered for use in CMOS based X-ray imaging devices, for various applications

Ανάπτυξη μεθοδολογίας για τη διάγνωση καρκίνου του μαστού με τεχνικές διπλής ενέργειας ακτίνων –Χ και ψηφιακής τομοσύνθεσης

Breast cancer screening and diagnosis in X-ray mammography rely on the detection and visualization of microcalcifications (μCs) and masses. The detection and visualization of μCs are relatively easy over a uniform tissue background. However, visualization of μCs could be obscured in mammograms by overlapping tissue structures. Dual energy (DE) imaging techniques can suppress the contrast between adipose and glandular tissues improving the detectability of μCs and masses. The current thesis is focused on the study of DE X-ray method applied on breast imaging, in order to improve the detection of breast calcifications. A simulation study was initially performed, based on analytical modeling, incorporating a modified radiographic X-ray unit combined with a high resolution CMOS sensor (pixel pitch of 22.5 μm). The calcification contrast-to-noise ratio of the DE subtracted images (CNRtc) was calculated for various skin entrance doses and calcification thicknesses using monoenergetic beams and polyenergetic X-ray beams. An experimental DE method was followed based on the proposed simulation exposure conditions. Custom-made homogenous and inhomogeneous breast phantoms and two different μC phantoms, as well as, the ACR mammography accreditation phantom were used. Post-process noise reduction was applied on the DE images in order to increase the contrast-to-noise ratio of the DE subtracted images (CNRDE). Further evaluation of the DE method was included using DE images obtained from a formalin-fixed breast cancer specimen. Also, three different μC types were compared using the proposed DE method. Finally, the potential to better visualize μCs using DE in digital breast tomosynthesis (DBT) was investigated. The TORMAM phantom was imaged and log-subtraction algorithm was applied to each pair of low-energy (LE) and high-energy (HE) slices after reconstruction. The various examined experimental setups demonstrated increased visibility of the μCs using the proposed DE method. Moreover, the DE images of breast specimen were directly comparable to the mammographic image and increased μC information was identified. The improvement in visualization of μCs, in the current method, is attributed to the use of higher kV X-rays from a modified radiographic unit with heavy filtering leading to larger spectral separation, while preserving MGD in acceptable levels. The use of post-processed DE images resulted in CNRDE values approximately 3 times that of the original DE image. In DE DBT images the μCs clusters were better defined than in the corresponding LE images. The initial results showed that DE DBT imaging could be a promising modality.Στην μαστογραφία ακτίνων-Χ, ο προσυμπτωματικός έλεγχος και η διάγνωση του καρκίνου του μαστού βασίζονται στην ανίχνευση και απεικόνιση των μικροαποτιτανώσεων (μCs) και των μαζών. Η ανίχνευση και η απεικόνιση των μCs σε ένα ομοιογενές υπόβαθρο είναι σχετικά εύκολη. Ωστόσο η απεικόνισή τους μπορεί να είναι δύσκολη σε μαστογραφίες με αλληλεπικαλυπτόμενες δομές. Οι τεχνικές απεικόνισης διπλής ενέργειας (DE) μπορούν να καταστείλουν την αντίθεση μεταξύ λιπώδους και αδενικού ιστού βελτιώνοντας την ανίχνευση των μCs και των μαζών. Η συγκεκριμένη διατριβή εστιάζει στη μελέτη της τεχνικής DE στην απεικόνιση μαστού, με στόχο τη βελτίωση της ανίχνευσης των μCs του μαστού. Αρχικά πραγματοποιήθηκε μια μελέτη προσομοίωσης με βάση την αναλυτική μοντελοποίηση, ενσωματώνοντας μια τροποποιημένη ακτινολογική λυχνία ακτίνων-Χ και έναν ανιχνευτή υψηλής ανάλυσης τύπου CMOS (μέγεθος pixel 22.5 μm). Υπολογίστηκε ο λόγος αντίθεσης προς θόρυβο στην τελική αφαιρούμενη εικόνα DE (CNRtc) για διάφορες δόσεις εισόδου και πάχη μCs χρησιμοποιώντας μονοενεργειακές δέσμες και πολυενεργειακές ακτίνες-Χ. Τη μελέτη προσομοίωσης ακολούθησε η πειραματική διαδικασία χρησιμοποιώντας τις βελτιστοποιημένες συνθήκες ακτινοβόλησης. Κατασκευάστηκαν ομοιογενή και ανομοιογενή ομοιώματα μαστού και δυο ομοιώματα μCs με διάφορα πάχη. Επίσης χρησιμοποιήθηκε και το ομοίωμα ACR. Στη συνέχεια εφαρμόστηκαν μέθοδοι μείωσης θορύβου στην τελική εικόνα DE για την αύξηση του λόγου αντίθεσης προς θόρυβο στην εικόνα DE (CNRDE). Πραγματοποιήθηκε περαιτέρω αξιολόγηση της μεθόδου χρησιμοποιώντας εικόνες DE από καρκινικό δείγμα μαστού σε φορμόλη. Επίσης, συγκρίθηκαν τρεις διαφορετικοί τύποι μCs μέσω της προτεινόμενης μεθόδου DE. Τέλος, διερευνήθηκε η δυνατότητα καλύτερης απεικόνισης των μCs με τη χρήση της μεθόδου DE και ψηφιακής τομοσύνθεσης μαστού (DBT). Απεικονίστηκε το ομοίωμα TORMAM και εφαρμόστηκε η μέθοδος σταθμισμένης λογαριθμικής αφαίρεσης σε κάθε ανακατασκευασμένη τομή. Οι διάφορες πειραματικές διατάξεις που εξετάστηκαν απέδειξαν οτι με τη χρήση της προτεινόμενης μεθόδου DE, βελτιώνεται η απεικόνιση και ανίχνευση των μCs. Επιπλέον, οι εικόνες DE του δείγματος μαστού ήταν άμεσα συγκρίσιμες με την αντίστοιχη μαστογραφία και παρατηρήθηκε βελτίωση στην απεικόνιση των μCs. Η βελτίωση οφείλεται στη χρήση ακτίνων-Χ υψηλότερων kV που οδήγησε σε μεγαλύτερη διαχωρισιμότητα μεταξύ των μέσων ενεργειών των φασμάτων ακτίνων-Χ χαμηλής και υψηλής τάσης λυχνίας, διατηρώντας ταυτόχρονα την MGD σε αποδεκτά επίπεδα. Η χρήση τεχνικών μείωσης θορύβου στην τελική εικόνα DE, οδήγησε σε αύξηση των τιμών CNRDE (περίπου 3 φορές πάνω). Στις εικόνες DE DBT τα όρια των μCs ήταν πιο σαφή συγκριτικά με την εικόνα χαμηλής ενέργειας. Τα αρχικά αυτά αποτελέσματα έδειξαν ότι η DE DBT είναι μια πολλά υποσχόμενη μέθοδος

Dual Energy X-ray Methods for the Characterization, Quantification and Imaging of Calcification Minerals and Masses in Breast

Dual energy (DE) technique has been used by numerous studies in order to detect breast cancer in early stages. Although mammography is the gold standard, the dual energy technique offers the advantage of the suppression of the contrast between adipose and glandular tissues and reveals pathogenesis that is not present in conventional mammography. Both dual energy subtraction and dual energy contrast enhanced techniques were used in order to study the potential of dual energy technique to assist in detection or/and visualization of calcification minerals, masses and lesions obscured by overlapping tissue. This article reviews recent developments in this field, regarding: i) simulation studies carried out for the optimizations of the dual energy technique used in order to characterize and quantify calcification minerals or/and visualize suspected findings, and ii) the subsequent experimental verifications, and finally, the adaptation of the dual energy technique in clinical practice

Mineral Characterization in Human Body: A Dual Energy Approach

Kidney and uteric stones are a common cause of pain and disturbance in numerous people worldwide, as they tend to reappear. There are several studies investigating the association of urolithiasis and nephrolithiasis with atherosclerosis, as patients suffering from the former diseases were found to have been diagnosed with atherosclerotic plaques. Hydroxyapatite and calcium oxalate are the most common mineral crystals found in both kidney/uteric stones and atherosclerotic plaques’ calcifications. Even though for stones smaller than 5 mm surgery is not recommended, the knowledge of the stone composition is an important tool for the physician in order to provide better treatment for the patient. The mineral crystal characterization of atherosclerotic plaques’ calcifications smaller than 3 mm (spotty calcifications) will assist the physician to limit the possibility of myocardial infraction and stroke, as the presence of hydroxyapatite indicates possible plaque rapture. To this aim, a dual energy (DE) X-ray method was developed in this work. The calcium/phosphorus mass ratio (mCa/mP) was determined through analytical simulations and the results were verified experimentally. Both monoenergetic and polyenergetic simulation studies were implemented for hydroxyapatite, calcium carbonate and calcium oxalate with thicknesses ranging from 0.50 to 3.00 mm, at 100 μm increments, to obtain the optimized irradiation conditions. The experimental verification of the proposed method was performed using an X-ray tube combined with a high resolution complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) detector. The Mann–Whitney U test indicated that statistically significant differences were found between the different types of minerals examined for thicknesses of 0.70 mm or higher

On the Response of a Micro Non-Destructive Testing X-ray Detector

Certain imaging performance metrics are examined for a state-of-the-art 20 μm pixel pitch CMOS sensor (RadEye HR), coupled to a Gd2O2S:Tb scintillator screen. The signal transfer property (STP), the modulation transfer function (MTF), the normalized noise power spectrum (NNPS) and the detective quantum efficiency (DQE) were estimated according to the IEC 62220-1-1:2015 standard. The detector exhibits excellent linearity (coefficient of determination of the STP linear regression fit, R2 was 0.9978), while its DQE peaks at 33% and reaches 10% at a spatial frequency of 3 cycles/mm, for the measured with a Piranha RTI dosimeter (coefficient of variation CV = 0.03%) exposure value of 28.1 μGy DAK (detector Air Kerma). The resolution capabilities of the X-ray detector under investigation were compared to other commercial CMOS sensors, and were found in every case higher, except from the previous RadEye HR model (CMOS—Gd2O2S:Tb screen pair with 22.5 μm pixel pitch) version which had slightly better MTF. The present digital imager is designed for industrial inspection applications, nonetheless its applicability to medical imaging, as well as dual-energy is considered and certain approaches are discussed in this respect

Luminescence Efficiency of Cadmium Tungstate (CdWO4) Single Crystal for Medical Imaging Applications

Background: In this study, the light output of a cadmium tungstate (CdWO4) single crystal was measured under various X-ray radiographic energies. Methods: A CdWO4 single crystal (10 × 10 × 10 mm3) was exposed to X-rays in the 50–130 kVp range. Measurements were evaluated against published data for single crystals of equal dimensions (CaF2:Eu and Lu3Al5O12:Ce). Since the crystal was examined for application in medical imaging detectors, the emitted optical spectrum was classified with respect to the spectral compatibility of numerous commercial optical sensors. Results: The luminescence efficiency (LE) was found to constantly increase with X-ray energy and was higher than that of CaF2:Eu for energies above 90 kVp. However, the efficiency of the previously published Lu3Al5O12:Ce was found to be constantly higher than that of CdWO4. The light emitted from CdWO4 can be optimally detected by certain charge-coupled devices (CCDs), amorphous silicon photodiodes, and photocathodes. Conclusions: The high density (7.9 g/cm3) of CdWO4 and the luminescence signal of this material make it suitable for medical imaging (such as dual energy), high-energy physics or for applications of scintillators in harsh environments